Contactless ignition system for internal combustion engine

ABSTRACT

A contactless ignition system is provided with an ignition charge discharge condenser for charging an induced voltage of a generating coil, a first switching element, triggered to conduct when an induced voltage of a generating coil reaches a predetermined level, for supplying a charged voltage into an ignition coil, and a trigger control condenser for charging induced voltages of the generating coil and the trigger coil, and triggering of the first switching element caused by an induced voltage of the generating coil is inhibited by a second switching element during a specified discharge time following charging of the trigger control condenser.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a contactless (non-contact)ignition system for an internal combustion engine for automaticallysubjecting ignition timing to spark advance control and sparkretardation control from a low rotational speed range to a highrotational speed range.

[0003] 2. Related Art

[0004] As a contactless ignition system for an internal combustionengine of the related art, for example, at the time of rotation of arotor having magnetic poles, a generating coil charges an inducedvoltage into an ignition charge and discharge condenser, and electricalcharge charged into the ignition charge and discharge condenser issupplied to an ignition coil through switching elements that areswitched by a voltage induced by a trigger coil.

[0005] In this type of contactless ignition system, if the rotationalspeed of the internal combustion engine, namely the rotational speed ofthe rotor, is increased, then together with that increase in speed thecharge discharge timing of the ignition charge discharge condenser isadvanced, and finally the rotational speed of the internal combustionengine is increased in excess of a set rotational speed and sometimesresults in damage to the engine.

[0006] Devices adopting a governor mechanism and devices utilizingelectronic control have therefore been proposed as devices forpreventing overspeed of an internal combustion engine.

[0007] However, the governor mechanism requires a large operating spacebecause of expansion and contraction effects while rotating integrallywith a crank shaft, and there is the drawback that lifespan is shorteneddue to mechanical operation.

[0008] Also, with an engine overspeed prevention device that useselectronic control, there is a problem that because complicatedelectronic circuitry is used it is not possible to realize costreduction.

SUMMARY OF THE INVENTION

[0009] The present invention has been conceived in view of the abovedescribed situation, and an object of the invention is to provide acompact and inexpensive contactless ignition system for an internalcombustion engine that can improve starting performance and horsepowerwhile causing advancement of ignition timing from low engine speed tonormal engine speed, and that can prevent engine overspeed by causingretardation of ignition timing at above normal engine speed.

[0010] In order to achieve this object, a contactless ignition systemfor an internal combustion engine of the present invention comprises arotor having magnetic poles arranged either side of a magnet, a corewith two legs, arranged opposite the rotor, wound with a trigger coil onthe one leg and with a generating coil on the other leg positionedopposite to the rotational direction of the rotor with respect to theone leg, an ignition charge discharge condenser for charging an inducedvoltage of the generating coil, a first switching element, triggered tobe conductive when an induced voltage of the generating coil has reacheda predetermined (specified) trigger level, for supplying a voltagecharged in the ignition charge discharge condenser to an ignition coil,a trigger control condenser for charging induced voltages of thegenerating coil and the trigger coil, and a second switching element forinhibiting a trigger of the first switching element caused by inducedvoltage of the generating coil for a specified time following charge ofthe trigger control condenser.

[0011] In the present invention, at the time of startup, since ignitiontiming of the internal combustion engine is advanced, kick back (aphenomenon where a piston is pushed back immediately after ignition andthe crankshaft rotates backwards due to piston speed being slow whenstarting) does not occur, and stable startup and increased speed can beexpected. Also, in a normal engine speed range, it is possible tosufficiently maintain horsepower of the engine by sufficiently advancingthe ignition timing. On the other hand, in a high engine speed region inexcess of the normal engine speed, since the ignition timing can beretarded there is the advantage that it is possible to prevent engineoverspeed.

[0012] As a preferred embodiment, it is possible for the secondswitching element to be a transistor that short-circuits the two ends ofthe trigger coil within a specified time of discharge of the triggercontrol condenser, to inhibit triggering of the first switching element.In this way, triggering of the first switching element can beimplemented using a low cost circuit structure.

[0013] As another preferred embodiment, it is possible for the triggercontrol condenser to comprise a time constant circuit for determining adischarge time constant of the trigger control condenser in order toachieve ignition timing retardation control. In this way, there is theadvantage that it is possible to select rotational speed of the enginethat causes the ignition timing retardation to start easily and withhigh precision by setting the discharge time constant of the timeconstant circuit.

[0014] As another preferred embodiment, it is possible to provide acircuit protection trigger circuit to trigger the first switchingelement in a high voltage below capacity voltage of the ignition chargedischarge condenser. In this embodiment, charge volume does not gobeyond capacity voltage of the ignition charge discharge condenser.Therefore, it is possible to prevent damages of each section of thecircuit including the ignition charge discharge condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a circuit diagram showing a contactless ignition systemfor an internal combustion system of an embodiment of the presentinvention.

[0016]FIG. 2 is a front elevation showing a partial cross section of theessential structure of the contactless ignition system of FIG. 1.

[0017]FIG. 3 is a timing chart showing voltage waveforms for eachsection of the circuit shown in FIG. 1 in a normal rotational enginespeed range.

[0018]FIG. 4 is a timing chart showing voltage waveforms for eachsection of the circuit shown in FIG. 1 in a high rotational engine speedrange.

[0019]FIG. 5 is a timing chart showing voltage waveforms for eachsection of the circuit shown in FIG. 1 in an engine overspeed range.

PREFERRED EMBODIMENT OF THE INVENTION

[0020] In FIG. 2, a rotor 3 constituting a contactless (non-contact)ignition system for an internal combustion engine of this embodiment hasa pair of magnetic poles 6 and 7 either side of a magnet 5 embedded in anon-magnetic body 4 such as a body of aluminum, for example. Part ofeach of the magnetic poles 6 and 7 are exposed at an outer surface ofthe rotor 3, and can be made opposite to end surfaces of two legs 8 a, 8b of a core 8 during rotation of the rotor 3.

[0021] The core 8 is an angular U shaped-member facing the rotor 3, anda generating coil 1 and a trigger coil 2 are respectively wound aroundthe legs 8 a and 8 b. The trigger coil 2 is wound around the one leg 8b, and the generating coil 1 is wound around the other leg 8 apositioned opposite to the rotational direction of the rotor 3 withrespect to the one leg 8 b. Surfaces of the legs 8 a and 8 b opposite tothe rotor 3 are formed in an arc shape so as to maintain a constantdistance from the rotor 3.

[0022] In FIG. 1, a diode 9, an ignition charge discharge condenser 10and a primary coil 11 a of an ignition coil 11 are connected in serieswith the generating coil 1, thus constituting a charging circuit forcharging a positive voltage induced by the generating coil 1.

[0023] The ignition charge discharge condenser 10 is connected in serieswith the anode and cathode of a thyristor 12, as a first switchingelement, a diode 15 and the primary coil 11 a of the ignition coil 11,and this series connection constitutes a discharge circuit fordischarging charged up charge of the ignition charge discharge condenser10. This discharge circuit functions to discharge charge charged intothe ignition charge discharge condenser 10 to the ignition coil 11 whenthe thyristor 12 is triggered and made to conduct.

[0024] A spark plug 13 is connected to the secondary coil 11 b of theignition coil 11, and an LC oscillation diode 14 for the primary side ofthe ignition coil 11 is connected between the anode and cathode of thethyristor 12.

[0025] A resistor 16 connects the gate of the thyristor 12 to the pointof connection between the cathode of the thyristor 12 and the diode 15.A series circuit comprising a resistor 17 and a diode 18 is connected inparallel to the diode 15 through the resistor 16.

[0026] On the other hand, a resistor 19, a diode 20, a trigger controlcondenser 21 and the diode 15 are connected in series to the two ends ofthe trigger coil 2. Also, a resistor 22 and a diode 23 are connected inseries between a circuit linking the generating coil 1 with the diode 9and a circuit linking the diode 20 with the trigger control condenser21.

[0027] Resistors 24 and 25 constituting a time constant circuit togetherwith the trigger control condenser 21 are connected in series to the twoends of the trigger control condenser 21, and the base of a transistor26, as a second switching element, is connected to the point ofconnection between these two resistors 24 and 25. The collector of thetransistor 26 is connected to a circuit linking one end of the triggercoil 2 and the diode 15. Also, the emitter of the transistor 26 isconnected to a circuit linking the generating coil 1 and the diode 9through a resistor 27 and a diode 28. The collector of the transistor 26is also connected to the gate of the thyristor 12 through the diode 18and the resistor 17. A reverse current prevention diode 29 is connectedto the two ends of the trigger coil 2. Also, a circuit protectiontrigger circuit 31 having a resistor 30 is connected between the circuitlinking the generating coil 1 with the diode 9 and the gate of thethyristor 12. The circuit protection trigger circuit 31 triggers thethyristor 12 in a high voltage below capacity voltage of the ignitioncharge discharge condenser 10.

[0028] Next, operation of the contactless ignition system for aninternal combustion engine having the above-described structure will bedescribed. First of all, if the engine is activated and the rotor 3rotates in the direction of arrow A in FIG. 2, voltages having thewaveforms shown in FIG. 3(a) and FIG. 3(b) are respectively induced inthe generating coil 1 and the trigger coil 2 on the core 8 opposite therotor 3. The induced voltage of the trigger coil 2 is generated laterthan the induced voltage of the generating coil 1. Of induced voltage inthe generating coil 1, a positive voltage is applied to the primary coil11 a of the ignition coil 11 through the diode 9 and the ignition chargedischarge condenser 10 and electric charge is charged into the ignitioncharge discharge condenser 10.

[0029] On the other hand, of voltage induced in the trigger coil 2,positive voltage rises later than the positive induced voltage of thegenerating coil 1, by a predetermined period, and this voltage chargesthe trigger control condenser 21 through the resistor 19 and the diode20, 15. The trigger control condenser 21 is also charged by the positiveinduced voltage from the generating coil 1, to give a charge voltagewaveform as shown in FIG. 3(c). After charging of the ignition chargedischarge condenser 10, if the gate voltage of the thyristor 12 reachesa specified level, namely if the induced voltage of the trigger coils 2reaches an initial trigger level LL shown in FIG. 3(a), the thyristor 12is turned on and electric charge of the ignition charge dischargecondenser 10 is supplied though the thyristor 12 to the ignition coil11. As a result, an ignition voltage is applied from the ignition coil11 to the spark plug 13, and a fuel air mixture inside the fuel chamberof the internal combustion engine is ignited. By repeating thisoperation, the engine is started and then increased in speed, andhorsepower, being the engine output, is increased by advancing theignition timing.

[0030] Then, in a process for changing induced voltage of the triggercoil 2 from positive to negative, charge having the charge voltagewaveform shown in FIG. 3(c) that has been charged into the triggercontrol condenser 21 is discharged through the resistors 24 and 25 andthe transistor 26 is turned on. As a result, the series circuit of thetransistor 26, the resistor 27 and the diode 28 shunts the generatingcoil 1, and during this time triggering of the thyristor 12 is inhibitedso the thyristor 12 is OFF.

[0031] Accordingly, when the engine speed becomes high beyond a normalspeed range, the generating cycle of the induced voltage of thegenerating coil 1 becomes short. The width of the induced voltage on thetime axis becomes wide, and, as shown in FIG. 4, the thyristor 12 istriggered late for a retardation width T1. Thereby, the discharge of thecharge voltage R of the ignition charge discharge condenser 10 begins tobe retarded. Specifically, as shown in FIG. 4, if the engine speedexceeds a normal engine speed corresponding to a set time constant ofthe time constant circuit, the ignition timing is gradually retarded,and as a result it is possible to prevent overspeed of the engine.

[0032] After starting the engine, from a low speed range to a specifiednormal speed range, reaching the normal speed NR, the ignition timing isnot affected by the time constant and is advanced rapidly together withincrease in engine speed. Accordingly, together with carrying out stablestartup of the engine, it is possible to prevent the occurrence of kickback (a phenomenon where a piston is pushed back immediately afterignition and the crankshaft rotates in reverse due to slow piston speedat the time of startup) caused by delay on cranking, and since ignitiontiming is advanced as much as possible in the normal engine speed rangeit is possible to sufficiently maintain engine horsepower. Also, byusing the trigger coil 2, it is possible to simplify the circuitstructure for ignition timing control.

[0033] On the other hand, if the engine speed becomes higher beyond thehigh speed range, the generating cycle of induced voltage of thegenerating coil 1 becomes shorter as shown in FIG. 5, and triggering ofthe thyristor 12 is inhibited when the transistor 26 turns on by thedischarge voltage of the trigger control condenser 21. Thereby,supplying the ignition coil 11 with ignition current is prevented, andit is possible to prevent overspeed of the engine. At the same time, thecharge voltage gradually rises in the ignition charge dischargecondenser 10. When the charge voltage reaches a specified level HL belowcapacity voltage of the ignition charge discharge condenser 10, triggercurrent flows at the gate of the thyristor 12 through the resistor 30.Thereby, the thyristor 12 turns on and electrical charge of the ignitioncharge discharge condenser 10 is discharged into the ignition coil 11,which makes perfect the protection of the ignition charge dischargecondenser 10 and other sections in the circuit.

1. A contactless ignition system for an internal combustion engine,comprising, a rotor having magnetic poles arranged either side of amagnet, a core with two legs, arranged opposite the rotor, wound with atrigger coil on the one leg and with a generating coil on the other legpositioned opposite to the rotational direction of the rotor withrespect to the one leg, an ignition charge discharge condenser forcharging an induced voltage of the generating coil, a first switchingelement, triggered to be conductive when an induced voltage of thegenerating coil has reached a predetermined trigger level, for supplyinga voltage charged in the ignition charge discharge condenser to anignition coil, a trigger control condenser for charging induced voltagesof the charging coil and the trigger coil, and a second switchingelement for inhibiting a trigger of the first switching element causedby induced voltage of the generating coil for a specified time followingcharge of the trigger control condenser.
 2. The contactless ignitionsystem for an internal combustion engine according to claim 1, whereinthe second switching element is a transistor for short-circuiting bothends of the trigger coil for a specified charging time of the triggercontrol condenser to prevent triggering of the first switching element.3. The contactless ignition system for an internal combustion engineaccording to claim 1, wherein the trigger control condenser constitutesa time constant circuit for determining a discharge time constant of thetrigger control condenser in order to perform ignition timingretardation control.
 4. The contactless ignition system for an internalcombustion engine according to claim 1, further comprising a circuitprotection trigger circuit to trigger the first switching element in ahigh voltage below capacity voltage of the ignition charge dischargecondenser.